In general, a battery is divided into a chemical battery and a physical battery, wherein the chemical battery is subdivided into a primary battery, a secondary battery, and a fuel cell. The secondary battery includes a nickel-cadmium (Ni—Cd) secondary battery, a nickel-metal hydride (Ni-MH) secondary battery, a Sealed Lead-Acid (SLA) secondary battery, a lithium-ion secondary battery, a lithium-polymer secondary battery, and a reusable alkaline secondary battery.
Above all, the lithium-ion secondary battery is a kind of organic electrolyte battery having stable properties in terms of high energy density, low-temperature property, storability, and so on, and thus is broadly used as a battery for portable computers. Here, the term “energy density” indicates how much energy is charged, and refers to a value dividing energy capacity by volume or weight.
The lithium-ion secondary battery may be exposed to a high-temperature environment beyond a working range, for instance the inside of a vehicle in the summer season, the heated room of a public bathhouse, an electric heating blanket, a microwave oven, etc., due to carelessness of a user. Further, the lithium-ion secondary battery may spontaneously be heated by an internal short, an overcharge, and the like.
In this manner, when being exposed to high temperature beyond a certain temperature or heated by spontaneous generation of heat, the lithium-ion secondary battery may lead to swelling, inflammation, or detonation.
Conventionally, in order to prevent the lithium-ion secondary battery from being damaged due to the generation of heat caused by a simple overcharge, the lithium-ion secondary battery is connected in series to a positive temperature coefficient (PTC) resistor, a resistance of which increases depending on the generation of heat of the lithium-ion secondary battery.
The PTC resistor inhibits current from flowing to the lithium-ion secondary battery when the lithium-ion secondary battery is overheated, thereby preventing the lithium-ion secondary battery from being charged further.
However, the lithium-ion secondary battery may generate heat due to a change in external environment, an internal short, an external impact etc. in addition to the overcharge. Further, the lithium-ion secondary battery can be heated when being exposed to a high-temperature environment. When the lithium-ion secondary battery is exposed to a high-temperature environment or generates heat in a charged state, it suffers from relatively easy generation of gas, which causes a swelling phenomenon, and in the worst case, detonation or inflammation.
Taking into consideration that the lithium-ion secondary battery generates heat due to a change in external environment, an internal short, an external impact, and so on, or is exposed to a high-temperature environment, there is an earnest need for development of technology capable of protecting the lithium-ion secondary battery.